Method of extrusion and extrusion billet therefor



United States Patent 3,147,156 METHOD OF EXTRUSION AND EXTRUSIGN BILLET THEREFOR George S. Foerster, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Original application May 13, 1960, Ser. No. 28,844. Divided and this application July 10, 1961, Ser. No. 122,622

2 Claims.

The invention relates to an improved method of preparing an extrude of magnesium-base alloy and more particularly relates to an improvement in the method of preparing an extrude of precipitation-hardenable magnesium-base alloy from particulated metal and to an improved extrusion billet.

For the purposes of the specification and claims a magnesium-base alloy is defined as an alloy containing at least 75 percent by weight of magnesium.

Heretofore extrudes exhibiting good mechanical strength have been prepared by co-extruding particulated metals such as particulate magnesium-base alloy ZK60 admixed with particulate magnesium-aluminum alloy or aluminum. According to U.S. Patent 2,659,131 such an admixture of particulated metals is placed in the container of a pre-heated ram extrusion press and promptly die-expressed at relatively low speeds below about 5 feet per minute, then heat treated after extrusion to bring about precipitation hardening. A serious drawback to this procedure is the necessity of employing low extrusion speeds and temperatures, the frequency of surface scoring of the extrude and the low ductility exhibited by the extrude.

It has now been found that, if the alloying constituents are heat treated while in intimate contact whereby a precipitation-hardened magnesium-base alloy is formed, prior to co-extrusion, substantial advantages are obtained.

The so obtained advantages are entirely unexpected because it was not known heretofore that precipitation hardened magnesium-base alloy could be readily worked after precipitation hardening. The more recent work on high strength alloys has been almost entirely centered on alloy systems which harden on being worked and are adversely affected when heat treated before extrusion. Therefore there has been a strong tendency to avoid heat treating extrusion billets before the extrusion thereof.

Appropriate alloying constituents for the present invention must meet the requirements that firstly, the final alloy contain at least 75 percent of magnesium, and secondly, that the other alloying constituents create problems in mutual alloying. Thus, the final alloy will contain at least 75 percent of magnesium and two or more additional alloying components that are mutually insoluble in solidified magnesium.

As used herein the term insoluble refers to solubility in solidified magnesium-base alloy.

This process applies to all magnesium systems which experience interference hardening, incompatibility or compound formation. In the simplest form of the invention one of the mutually interfering alloying elements is employed as a component of a magnesium-base alloy and the other, desirably the more rapid diffusing of the two, is used in unalloyed form. For example, thorium may be used as a magnesium-base thorium-containing alloy and aluminum may be alloyed therewith according to the method of the invention.

In other modifications of the invention one of the mutually interfering alloying elements is employed as a component of a magnesium-base alloy and two or more alloying components interfering therewith are employed either as physical mixtures, or as alloyed together. The mutually interfering elements may also be brought to- 3,147,156 Patented Sept. 1, 1964 gether as components respectively of a magnesium-base alloy and a magnesium alloy if desired but the dilution of the interfering substances in the additional magnesium increases the heating time required for the diffusion process necessary for precipitation hardening and decreases the concentration of the solid-insoluble precipitates in the product of the invention.

Aluminum may be alloyed by the process of the invention with a magnesium-base alloy containing zirconium. Aluminum metal or magnesium alloys such as those containing from 20 to 30 percent by weight of aluminum may be employed as the source of aluminum. Mag nesiurn-base alloy containing zirconium may be alloyed with binary alloys or physical admixtures of aluminum and silicon, or, of aluminum and zinc. Other possible combinations are tabulated as follows:

Mutually Insoluble Combinations Component of magnesiumbase alloy: Other components 1 Zr Sn, Si, Zn Mn Al, Si, Zr Th A1 MM Al Li Al Ca Al H Employed singly or in combination or as a magnesium The magnesium-base alloy employed may also contain non-interfering components which impart desired properties such as ductility, corrosion resistance or higher mechanical strength. As an example, magnesium-base alloy containing up to 0.8 percent zirconium and at least one of the following: up to 4 percent of zinc, up to 6 percent of silver, up to 1 percent of calcium, up to 4 percent of rare earth, up to 4 percent of thorium, up to 5 percent of lithium, may be admixed with aluminum or magnesium-aluminum alloy, and heat treated and extruded according to the invention.

All the metals are employed in particulated form. The magnesium-base alloy is conveniently used as atomized pellets such as those prepared according to U.S. Patent No. 2,676,359. The other metals are generally best used in finely divided form such as that passing about a No. 325 sieve (U.S. Sieve Series). Larger sizes tend to make complete precipitation hardening more difficult, for example, by requiring a longer heat-treating period.

The proportions of each of the mutually interfering components employed in the process of the invention are not sharply critical. It is essential that a sufiicient amount of each be present to cause formation of a solid insoluble precipitate throughout the magnesium-base alloy. When processed according to the present invention with 1 percent by weight of aluminum, a magnesiumbase alloy containing as small a proportion of zirconium, such as 0.08 percent by weight, is found to have surprisingly increased strength properties, compared to a magnesium-base alloy containing either the aluminum or zirconium content alone. It is very desirable that the mutually insoluble component or components employed which are not a part of the initial magnesium-base alloy should be used in a small enough particle size and intimate enough dispersion that it will diffuse into the magnesium-base alloy in reasonable times at heat treating temperatures.

The magnesium-base alloy containing one of the mutually insoluble alloying components is brought into intimate contact with the additional insoluble component or components mainly in one of two ways.

The metals to be alloyed according to the invention are thoroughly blended and admixed, While in particulate form, as by tumbling the particles in a cylindrical container for 15 minutes or more. The thoroughly blended admixture is then placed in the preheated container of a die-extrusion press having a cover plate over the internal face of the die and the particles compacted under the final extrude does not hot short and also whereby sufiicient solid insoluble material is formed to significantly increase the properties of the extrude.

On the other hand, heat treating for overly extended periods tends to result in grain growth of the magnesium 5 heat and pressure to a coherent mass, or extrusion billet. and agglomeration of the solid insoluble material where- Thereafter the so-formed compact is ejected from the by maximum strength is not achieved. press. Typically a compact is formed at 500 to 800 F. The extrusion billet may be machined to a smaller under a pressure of about 50 tons per square inch. size, if necessary, to permit easy insertion into the ex- As a modification of the compacting process of formtrusion container. ing an extrusion billet the admixture may also be pre- The heat treated metal, whether in the form of an extruded at low reduction ratios such as 5 to 1, and at extrusion billet or particulate metal, is then extruded speeds of 2 feet per minute or less and desirably with at temperatures and reduction ratios well understood in a low container temperature to avoid hot shorting. As the magnesium metal art. Extrusion speeds, however, an example, pre-extrusion may be carried out at 600 may be radically increased from about 1 or 2 feet per to 700 F. with a container temperature of 600 F. and minute, heretofore used in the extrusion of such parat a speed of about 1 foot per minute. ticulate admixtures, to speeds as high as 100 feet per In another manner of bringing the materials into intiminute. mate contact the magnesium-base alloy in solid par- If desired, the extrusion billet formed in the process ticulate form may be dipped into, or sprayed with, the of the invention may be placed in a close-fitting sleeve other metal or alloy in molten form, or gas plated or formed of either a conventional magnesium-base alloy vacuum metallized or peen plated whereby a thin film or an aluminum-base alloy and transformed into rolled of the other metal or alloy is deposited on substantially form by passing it repeatedly, while at an elevated temeach particle of the magnesium-base alloy. An advanperature, between the rolls of a mill. The extrusion billet tage of the plating process is that the plated particles may also be worked in other ways such as by forging it can be heat treated in particulated form if desired, in a manner well understood in the art. and thereafter extruded into final form thus avoiding a E:cai7zples.To illustrate the improved process of the compacting or pre-extrusion step. invention various pelletized magnesium-base alloys con- The so-called compact or pre-extrusion, or the plated taining zirconium and having a particle size of about particles described above, are then heat-treated for an 20 to 140 mesh (US. Sieve Series) were thoroughly extended period to cause diffusion of the mutually inadmixed with fine aluminum powder passing a 325 mesh soluble alloying components whereby they meet and form i ve (US. Sieve Series). The mixtures were each comsolid insoluble particles, generally as intermetallic compacted into extrusion billets at a temperature of about pounds. Heat treating the metals at 700 to 900 F. for 650 F. and under a pressure of about 50 tons per periods of 12 to 48 hours is generally adequate for the square inch. The extrusion billets were each heat treated purposes of the invention, though shorter times may be for 16 hours at a temperature range of 750 to 800 F. used for mixtures formed from extremely fine particu- The so-treated billets were then scalped to reduce their late material. The most advantageous temperatures and d mensions slightly so they would fit into the 3 inch times vary somewhat with the magnesium alloy system diameter container of a ram extrusion press. The billets used and with the diffusion rates and particle sizes of w re a h expr hr gh a die-opening A6 y /1 interfering alloying components. The heat-treating coninch. The container temperature was 600 F. and the d1t1ons should be drastic enough to cause sufiicient difstrip was extruded at a temperature of 650 F. Extru- -fusion into the magnesium-base alloy of any mutually sion rates are shown in the table. The mechanical propinsoluble components originally external thereto that erties of the so-treated extrudes were determined exundesired compounds, such as brittle magnesium aluperimentally. The test results and the compositions used mmum intermetallic compound, are dissociated whereby are listed in Table I. One of the extrudes was given a Table I Composi- Composition of Physical properties, tionofmix- Mg-base alloy, Extrusion 1000sp.s.i.

turc, weight percent speed Per- Run weightfer ft./minute cent E No. cent 1 Zn Zr TYs CYS TS 0.25 1 0.24 4 40 29 47 0. 25 1 0. 24 100 4 40 26 47 0.5 1 0.24 100 5 41 31 48 1 1 0. 24 50 4 41 36 4s 1 1 0. 24 100 6 42 33 48 2 1 0.24 100 9 41 40 4s 2 1 s0. 24 100 12 41 40 48 3.6 1 so. 24 50 s 45 42 51 3. 6 1 S0. 24 100 8 44 43 51 4.4 1 s0. 24 10 47 44 53 6.2 1 s0. 24 40 s 43 46 54 1 1 0.05 11 25 14 3s 1 1 0.08 100 4 41 22 40 1 1 0.32 100 10 41 39 4s 1 1 0. s4 50 6 4s 4s 55 1 1 0.64 100 s 44 45 51 2 4.3 0.64 40 4 50 51 56 2 4. 3 0. 64 T5 40 6 52 54 49 2 0.57 100 6 43 45 54 1 Balance magnesium-base alloy.

2 Balance magnesium.

3 1.3 percent Al, 0.3 percent Mn (AZll).

Percent E=Percent elongation in 2 inches.

TYS=Tensile yield strength.

CYS=Compression yield strength.

TS=Ultimate tensile strength.

T5= Standard ASTM heat treatment, that was used after die-expression of cxtrudc. S=S10ved, only particles passing number 100 sieve were used.

Standard ASTM heat treatment, T5, which consisted of heating the extrude for 24 hours at 300 F. The properties of the so-treated extrude are listed as Run No. 18.

For purposes of comparison extrudes containing zinc and zirconium but not aluminum, and, aluminum and zinc but not zirconium were prepared and the properties were determined. The properties are listed in Table I. Also listed for comparison are the properties of an extrude formed by co-extruding magnesium-zirconium alloy with aluminum metal by a process not according to the meth- 0d of the invention.

In a second series of experiments atomized magnesiumbase zirconium alloy, containing one or more additional alloying components, was thoroughly admixed with fine particulate aluminum. The were compacted, heat-treated, scalped and extruded in the same manner as the admixtures tested in the first series of experiments. The compositions used, the extrusion speeds and the physical properties of the resulting extrudes are listed in Table II.

In a third series of experiments still an additional embodiment of the invention was carried out. Pellets of magnesium-base alloy containing zirconium were admixed with pellets of magnesium-aluminum alloy and the composition was compacted, heat-treated, scalped and extruded in the manner described in the first series of experiments. The physical properties of the resulting extrudes are determined and are listed in Table III.

so-prepared admixtures 15 experiment pellets of magnesium-base alloy were admixed with aluminum pellets. The admixture was then tumbled in a cylindrical container to peen plate the pellets with aluminum. Both of the above compositions were compacted, heat-treated, scalped and extruded in the manner described in the first series of experiments. The physical properties of these extrudes were determined and are also listed in Table III.

Among the advantages of the invention are the sizeable increases in mechanical strength, ductility and permissible extrusion speed, as well as the freedom from hot shorts and surface imperfections in the extruded material produced according to the method of the invention.

This is a divisional application of copending application Serial No. 28,844, filed May 13, 1960.

I claim:

1. An improved extrusion billet formed by preparing an intimate admixture consisting essentially of (1) particulate magnesium-base alloy containing at least one first alloying component and (2) at least one additional alloying component in finely divided form which is mutually solid-insoluble with each said first alloying component in said magnesium-base alloy, subjecting the said admixture in a closed vessel to a pressure and a temperature less than extrusion conditions but sufiicient to cause the particles of the admixture to become welded together into a coherent pre-extrusion mass, and subsequently heat treating the said coherent mass whereby the said magnesium- Table II Composi- Composition of Physical tion of Mg-base alloy, Other Extrusion properties, Run mixture, Weight percent compo- Weight speed, Percent 1000s p.s.i. N 0. weight nent (s) percent ft./minute E percent metal Al Zr Zn TYS CYS TS 2 2 100 4. 5 48 46 54 2 1 2 46 44 52 2 3 100 6 44 49 56 2 2 100 8 46 54 2 100 10 49 4a 55 2 g 70 e 46 4s 53 1 3. 1 6 46 48 53 1 3. 1 T5 20 4 47 51 55 1 5. 6 15 4 48 52 2 2. 8 100 3 49 49 53 2 5. 5 7 49 52 56 1 3. 3 5O 9 47 52 57 2 3. 3 30 8 49 56 58 2 3. 3 T5 30 4 50 59 1 Balance magnesium-base alloy. 2 Balance magnesium.

T5=See reierence note at end of Table I.

Table III Aluminum source Composition of Mg-base alloy Extrusion Physical properties, Bun used, weight speed, Percent 10005 p.s.i. No. percent ft./ E

Metal Weight Particle Mesh minute alloy percent 1 form size 3 Zn Zr TYS CYS TS Mg 4 Al... 25 Atomized 20 1 0.24 100 5 39 30 46 pellets. Mg 10 AL. 10 20 1 0. 24 100 6 32 17 39 Mg 10 A 10 1 0.24 100 5 39 28 46 Mg 15 AL. 7 70 1 0.24 100 5 32 16 41 Mg 33 AL. 8 20 1 0. 24 100 2 25 16 31 Mg 33 AL. 3 70 1 0.24 50 4 34 25 42 Mg 33 AL. 3 70 1 0 24 100 2 32 24 39 A 1 325 1 4 0.5 100 4 42 35 50 A1 2. 6 Atomized 325 1 5 0.24 100 5 38 29 45 pellets.

1 Balance of the mixture magnesium-base alloy. 2 Number of sieve passed. 3 Balance magnesium.

4 Chips machined from ingot; dimensions averaged about 0.020 x x 36 inch. 6 Magnesium-base alloy mixed with the Al pellets and tumbled in cylindrlcal container to peen plate the pellets with A1.

In an additional experiment aluminum flake passing a 325 mesh sieve was admixed with chips of magnesiumbase alloy machined from an ingot. In still an additional base alloy therein is precipitation hardened thereby to provide an extrusion billet adapted to be extruded at relatively high speeds.

2. Precipitation hardened magnesium-base alloy in particulate form adapted for extrusion at relatively high speeds, said precipitation hardened magnesium-base alloy containing (1) at least 75 percent by weight of magnesium and (2) a uniformly dispersed solid insoluble phase formed by precipitation hardening reaction within the alloy between at least two alloying constituents that are mutually insoluble in solidified magnesium.

References Cited in the file of this patent UNITED STATES PATENTS Bevilard Oct. 20, 1942 Leontis et al Nov. 17, 1953 OTHER REFERENCES 

1. AN IMPROVED EXTRUSION BILLET FORMED BY PREPARING AN INTIMATE ADMIXTURE CONSISTING ESSENTILLY OF (1) PARTICULATE MAGNESIUM-BASE ALLOY CONTAINING AT LEST ONE FIRST ALLOYING COMPONENT AND (2) AT LEAST ONE ADDITIONAL ALLOYING COMPONENT INFINELY DIVIDED FORM WHICH IS MUTUALLY SOLID-INSOLUBLE WITHEACH SAID FIRST ALLOYING COMPONENT IN SAID MAGNESIUM-BASE ALLOY, SUBJECTING THE SAID ADMIXTURE IN A CLOSED VESSEL TO A PRESSURE AND A TEMPERATURE LESS THAN EXTRUSION CONDITIONS BUT SUFFICIENT TO CAUSE THE PARTICLES OF THE ADMIXTURE TO BECOME WELDED TOGETHER INTO A COHERENT PRE-EXTRUSION MASS, AND SUBSEQUENTLY HEAT TREATING THE SAID COHERENT MASS WHEREBY THE SAID MAGNESIUMBASE ALLOY THEREIN IS PRECIPITATION HARDENED THEREBY TO PROVIDE AN EXTRUSION BILLET ADAPTED TO BE EXTRUDED AT RELATIVELY HIGH SPEEDS. 